Due to the relatively high cost of liquid hydrocarbon fuels and fuel gas, wood burning and coal burning stoves have recently come back into vogue and are employed in a great many homes for providing the basic heat to those homes. With the advent of the modern type wood burning or coal burning stoves which are essentially air tight except for the controlled entry of primary and/or secondary air to the combustion area, the time for burning a full load of wood fuel has been extended and lasts well through the night. Such combustion provided by these stoves is highly efficient, and the cost of heating residential homes has been reduced considerably from that experienced in heating by conventional oil fired and gas fired furnaces.
Attempts have been made to provide such solid fuel burning stoves and furnaces, an arrangement for feeding both primary and secondary air, the primary air being directed to the area of primary combustion, while secondary air flow is directed to the area where the ashes reside for insuring complete combustion of those resulting products of combustion as well as the complete combustion of combustible elements carried by air streams circulating within the stove or furnace.
In order to maximize the efficiency in the burning of solid fuels such as wood or coal, attempts have been made to produce a downdraft type of action in which the hot gases are directed downwardly from the area of primary combustion and by way of baffles, prevented from passing vertically upwardly through the unburned portion of the fuel prior to escaping through the stack. This permits more efficient thermal radiation to the room interior from the various walls of the burner as well as tending to limit the burning rate. Absent some type of control scheme, there is a great fluctuation in the BTU output of the burner. During intitial and early combustion, only a portion of the wood or coal is burning, and the heat is rather limited, while as the solid fuel burns upwardly, at some point in time, the major portion of the fuel stacked vertically within the heater is under combustion with an excessive amount of heat being radiated to the room or building structure housing the burner. Further, as the load of fuel is consumed, there is a time when only a small amount of that fuel remains unburned, and at that point the temperature drops, and the heat produced is insufficient to maintain proper temperature relative to the load provided by the building. Further, conventional solid fuel heaters, such as stoves or furnaces, tend to discharge a large amount of the heat up the stack where it is wasted to the building exterior through the stack, chimney, etc.
It is a primary object of the present invention, therefore, to produce an improved solid fuel heater in the form of a wood burning stove or furnace in which the burning of the fuel and the BTU output is controlled by separate adjustment of primary and secondary air through a thermostatically controlled damper, and wherein the heater is of the down draft type to promote combustion only of the bottom of the solid fuel stack within the burner.
It is a further object of the present invention to provide a downdraft, primary/secondary air type heater which insures the complete combustion of the solid fuel greatly reducing the mass of the ashes which must be periodically removed from the bottom of the burner.
It is a further object of the present invention to provide an improved solid fuel heater which employs a plurality of tubes for preheating the primary and secondary air flow prior to discharge of that air into the primary and secondary combustion areas of the heater.